%0 Journal Article
%T Niobium Pentachloride Activation of Enone Derivatives: Diels-Alder and Conjugate Addition Products
%A Mauricio Gomes Constantino
%A Valdemar Lacerda J¨˛nior
%A Gil Valdo Jos¨¦ Da Silva
%J Molecules
%D 2002
%I MDPI AG
%R 10.3390/70500456
%X Niobium pentachloride has proven to be a powerful activating agent for Diels-Alder or conjugate addition reactions of cycloenones. The Diels-Alder product was obtained only with an unsubstituted enone (cyclohexenone) and the highly reactive diene cyclopentadiene; substituents in the b-position of enones seem to prevent Diels-Alder reaction: oxygenated substituents favor the formation of vinyl chlorides (ethyl ether or dichloromethane as solvents) or enol ethers (ethyl acetate as solvent), while a methyl substituent prevents any kind of transformation with NbCl5. Less reactive dienes, furan and 2-methylfuran gave the conjugate addition products of the furan ring to the enone system.
%K Niobium pentachloride
%K Lewis acid
%K Diels-Alder reaction
%K vinyl chlorides
%U http://www.mdpi.com/1420-3049/7/5/456